The present invention relates to supervisory apparatus and technique and, more particularly, to a scheme that is capable of continuously supervising a public address system so as to ascertain whether there are faults such as opens or shorts due to failure of the wiring, that is, of the lines of the system, and also whether or not there is any failure connected with the speaker structures.
In general, it has been known to provide certain supervisory techniques in connection with the operation of public address systems or the like. These techniques are provided because it is often extremely important to know in certain kinds of systems that are to be relied on for transmitting crucial emergency or warning signals to occupants of a building that the systems remain capable of functioning properly at all times. To this end, it is common to transmit a supervisory tone or the like -- generally above the normal hearing spectrum -- and to monitor any substantial impedance changes due to open or short circuit conditions.
However, a fundamental problem occurs in the attempt to supervise or monitor a public address system in that the conventional speaker impedances are very slight, being of the order of 8 ohms, and since such small impedance speakers are connected in parallel it is virtually impossible to tell, within the context of a standard two-wire transmission loop, that a failure has occurred in the speaker itself; that is to say, somewhere within the coil structure of the speaker or the associated transformer, rather than in the wires forming the loop. Thus, the majority of prior art systems of simple construction cannot successfully ascertain and pin-point a failure within a speaker of a public address system since they are designed chiefly to sense only a substantial change in impedance, and concomitant change of current, in the transmission loop.
Accordingly, it is the major object of the present invention to enable supervision of a public address system such that any fault in the lines or transmission loops or paths, including failures within the speakers themselves, can be pin-pointed.
Another object is to accomplish the preceding object with a minimum of cost.
Another object is to realize the supervision of a public address system in such a way that only three wires or lines are required to be extended to the speakers.
The above and other objects are fulfilled and implemented by a primary or principal feature of the present invention. In accordance with this feature, individual transmission loops are provided to each of a plurality of zones for the public address system. Only three wires or lines are extended from a central station to each of these zones; nevertheless, complete supervision of the wiring or lines to the speaker stations within each of the zones, as well as monitoring or supervision of each of the speaker coils and associated transformers, is accomplished.
In accordance with a more specific feature of the present invention, a high frequency generator, that is, one capable of generating a frequency above the normal audible range, for example, approximately 25,000 cycles, is connected to a suitable amplifier at a central panel or station. At the same panel, a speaker wiring supervision means is provided and is connected to each of the zones in the public address system. The speaker wiring supervision means includes an arrangement which response to either a short or open anywhere in the wiring and, by additional means to be described, responds to a fault in the speaker itself. The supervision means is provided at its output with a trouble light or other signal. As a result, the operator is alerted to such failure and can proceed to the zone indicated by the particular trouble lamp, where be can then ascertain the particular location within that zone at which the fault has occurred.
In accordance with the above, any fault in the wiring, whether it be an open or short, will be detected. Moreover, there is included in the system, for the specific purpose of supervising or monitoring faults within the speakers themselves, a special module or assembly at each speaker location in each of the zones. Thus, for each speaker a detection arrangement is provided so as to sense whether or not the speaker coil is operative. This mechanism includes a magnetic pick-up spaced adjacent the speaker coil and connected to an amplification system and thence to a relay which is deactivated in the event that the speaker coil is sensed as either short or open. Operation of such relay permits the open or short circuited speaker coil to register or indicate that it is in a fault state. In other words, that speaker acts as any other failure or fault would in respect to the effect on the supervision means at the central station. However, a continuous path remains for transmission of audio frequencies. Thus, corrective action can be taken and the fault can be pin-pointed by reason of the fact that, despite the fault in a given speaker or speakers, an audible signal can be transmitted over the remaining speakers of that zone.
Other and further objects, advantages and features of the present invention will be understood by reference to the following specification in conjunction with the annexed drawings, wherein like parts have been given like numbers.